IMPACT OF WATER DROPS ON THE VISIBLE RADIATION TRANSMITTANCE OF GLAZINGS UNDER OUTSIDE RADIANT CONDITIONS

Abstract Experimentally determined directional-hemispherical transmittances for visible radiation were used to calculate the effect of condensate on the hemispherical–hemispherical transmittance values under diffuse radiant conditions for single glass and polyethylene. The hemispherical–hemispherical transmittances were determined in the horizontal plane for different inclinations of both glazing materials assuming a completely overcast sky and a clear sky. In all cases, condensate was found to reduce the transmittance. Under an overcast sky, the transmittance of single glass was reduced by the presence of condensate from 8 up to 13% (on a relative scale) for increasing inclination angles of the glass plate, while for the polyethylene film, the transmittance reduction due to condensate decreased from 20 down to 13%. Under a clear sky, depending on date, time, and orientation of the glazing material, the transmittances of single glass and polyethylene were reduced by between 6 and 15% and by between 8 and 21%, respectively, due to the presence of condensate. These results revealed that the impact of the presence of condensate on the transmittance of a glazing cannot be omitted from design and performance calculations of solar energy systems.

[1]  Jan Pieters,et al.  Effect of Latent Heat Phenomena on Thermal Insulation and Inside Climate of Greenhouses , 1998 .

[2]  P. V. Nijnatten,et al.  Determination of directional optical properties of an electrochromic device , 1997 .

[3]  H. Fechner,et al.  Solar Air Collectors — Investigations On Several Series-Produced Collectors , 2000 .

[4]  D. Inan,et al.  A solar still with minimum inclination, coupled to an outside condenser , 1999 .

[5]  M. G. Hutchins,et al.  Angular-dependent spectral optical properties of architectural glazings: results of an interlaboratory comparison of measurements , 1993, Optics & Photonics.

[6]  A. Roos,et al.  Modelling the angular behaviour of the total solar energy transmittance of windows , 2000 .

[7]  U. M. Peiper,et al.  Outdoor Testing of the Condensation Characteristics of Plastic Film Covering Materials Using a Model Greenhouse , 1994 .

[8]  A. Roos.  Optical characterization of coated glazings at oblique angles of incidence: measurements versus model calculations , 1997 .

[9]  M. Rubin,et al.  Models for the angle-dependent optical properties of coated glazing materials , 1999 .

[10]  Wolfgang Graf,et al.  Measurement of the hemispherical reflectance and transmittance at variable angles of incidence , 1995, Optics & Photonics.

[11]  Gunnar A. Niklasson,et al.  Angular selective window coatings: theory and experiments , 1997 .

[12]  C. Hsieh,et al.  The effect of dropwise condensation on glass solar properties , 1977 .

[13]  U. M. Peiper,et al.  A Model Greenhouse for Testing the Role of Condensation, Dust and Dirt on the Solar Radiation Transmissivity of Greenhouse Cladding Materials , 1998 .

[14]  R. I. Edwards,et al.  Transmission of solar radiation in a large-span East-West glasshouse: II. Distinction between the direct and diffuse components of the incident radiation , 1965 .

[15]  A. Roos,et al.  Evaluation of predictive models for the angle-dependent total solar energy transmittance of glazing materials , 2001 .

[16]  Joakim Karlsson,et al.  Angle-resolved optical characterisation of an electrochromic device , 2000 .

[17]  A. Narayan,et al.  Chapter 229 – Computer Based Thermal Modelling of Double Condensing Chamber Solar Still , 2000 .

[18]  Gunnar A. Niklasson,et al.  Angular selective optical properties of thin films: Measurement of polar and azimuthal transmittance , 1996 .

[19]  Jan Pieters,et al.  Light transmission through condensation on glass and polyethylene , 1997 .

[20]  W. Platzer.  Directional-hemispherical solar transmittance data for plastic honeycomb-type structures , 1992 .

[21]  I. Pollet,et al.  Effect of inclination angle on the light transmittance of condensate covered homogeneous thin transparent materials , 2002 .

[22]  Brian J. Briscoe,et al.  The effect of surface fog on the transmittance of light , 1991 .

[23]  J. Monteith,et al.  Principles of Environmental Physics , 2014 .

[24]  Jan Pieters,et al.  Condensation and Radiation Transmittance of Greenhouse Cladding Materials: Part 1, Laboratory Measuring Unit and Performance , 1999 .

[25]  I. Pollet,et al.  PAR transmittances of dry and condensate covered glass and plastic greenhouse cladding , 2002 .